Introduce SubframeNavigationFilteringThrottle

content/browser/frame_host/navigation_handle_impl.cc

Index: content/browser/frame_host/navigation_handle_impl.cc
diff --git a/content/browser/frame_host/navigation_handle_impl.cc b/content/browser/frame_host/navigation_handle_impl.cc
index 74e0b202c6f005ffc79bb32c909b01bb847c83f2..a13f07508316a9c97860b7a1d95e07b230147bd9 100644
--- a/content/browser/frame_host/navigation_handle_impl.cc
+++ b/content/browser/frame_host/navigation_handle_impl.cc
@@ -456,6 +456,10 @@ NavigationData* NavigationHandleImpl::GetNavigationData() {
   return navigation_data_.get();
 }
 
+bool NavigationHandleImpl::IsCancellingForTesting() {
+  return state_ == CANCELING;
+}
+
 const GlobalRequestID& NavigationHandleImpl::GetGlobalRequestID() {
   DCHECK(state_ == WILL_PROCESS_RESPONSE || state_ == DEFERRING_RESPONSE ||
          state_ == READY_TO_COMMIT);